Same here! i installed Steam on multiple macs (imac, macbooks...), allways the same problem! Videos wont play in Full-Screen. This problem is old and with every Steam-Update i hoped they fixed it. No luck sofar :(

Same problem. Some one in a similar thread said it was due to a Flash problem and not the fault of the Steam, but I can play fullscreen movies on the Steam website, it is only the Steam client that crashes.

I posted this in September, it's now March... I think Steam has forgotten about us Mac users. Come'on guys! I know Flash sucks, but it can't be that difficult of a fix, is it? It's just full screen. :-/